A 9-year-old boy presents with bleeding gums, poor wound healing, and perifollicular hemorrhages. Biopsy of healing skin shows defective collagen fiber maturation. The biochemical defect involves:
- A Impaired prolyl hydroxylase activity because ascorbate is unavailable to keep the enzyme's iron in the ferrous state ✓
- B Failure of lysyl oxidase to form desmosine cross-links due to copper deficiency
- C Defective cleavage of procollagen N-terminal propeptides by procollagen peptidase
- D Reduced transcription of the COL1A1 gene leading to diminished type I collagen synthesis
Correct answer: A. Impaired prolyl hydroxylase activity because ascorbate is unavailable to keep the enzyme's iron in the ferrous state
Explanation
This is scurvy. Prolyl hydroxylase (and lysyl hydroxylase) require Fe2+, molecular oxygen, and ascorbate; ascorbate reduces the ferric iron that accumulates during the reaction, keeping the enzyme active. Without hydroxylation, the triple helix is unstable at body temperature and fibers are defective. Lysyl oxidase cross-linking needs copper, not ascorbate, and peptidase cleavage is unrelated to vitamin C.
Reference: Lippincott Illustrated Reviews: Biochemistry, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.